Inside, owners will receive one of the latest versions of the Android OS, plus a tweak to the camera application. As stated by SamMobile, who are running an unofficial build of the update, the tweak will bring an easier adjustment UI for the exposure level in any given picture. This feature is already available on both devices through the dedicated Pro mode, but when updated, it is said to be easier to use, and more straightforward for endusers.
Of course, the June timeline may just be for overseas variants of the phones, meaning US users who purchased their phone through a carrier may have to wait a tad bit longer to receive Android 5.1.
Regardless, we will keep you posted on when to expect your update.